1. The Prior Art
In U.S. Pat. No. 3,783,249, granted Jan. 1, 1974, there is disclosed a coded pulse generation system which includes a coded card and code reader. The card is provided with a plurality of axially straight helically twisted magnetic wires disposed parallel to each other and extending transversely of the card. Each of the wires is treated to form a shell and a central core, with the shell having the capacity to be permanently magnetized in an axial direction and having high coercivity. The core, by contrast, has relatively low coercivity. Both the shell and the core are magnetically anisotropic, with an easy axis of magnetization parallel to the axis of the wire. The wire is magnetized by subjecting it to an external magnetic field. Since the relatively hard shell has a retentativity and coercivity greater than that of the relatively soft core, when the external magnetic field employed to magnetize the wire is removed, the shell retains its magnetization and couples or captures the core by magnetizing it in an axial direction opposite to the direction of magnetization of the shell. Thereby, the core forms a magnetic return path or shunt for the shell, and a domain wall interface between the core and the shell.
According to the disclosure of the aforesaid patent, when each of the wires is subjected to an external magnetic field of greater magnitude than the field of the shell, and having a polarity opposite to that of the shell, such as by bringing a permanent magnet into close proximity to the wire, as the external field increases to a certain point, it overcomes the coercivity of the wire shell over the core, thereby capturing the core from the shell by abruptly reversing the flux direction of the core through the process of nucleation of a magnetic domain. Conversely, when such external magnetic field is removed from the vicinity of the wire, the reversal of the field direction of the core results in an abrupt change in the magnetic flux surrounding the wire. If a coil is placed adjacent to the wire, as the permanent magnet is thus brought into close proximity to, and removed from, the vicinity of the wire, it will be found that current pulses are induced in the coil by abrupt changes in the magnetic field. The said patent further teaches the utilization of this magnetically inducted effect in a coded passcard system. The manner in which bi-stable ferro-magnetic wire may be provided, is the subject of a further U.S. Pat. No. 3,820,090, issued June 25, 1974, on an application of the same inventor.
Among the ways in which the magnetic and inductive principle so described in U.S. Pat. No. 3,783,249 has been utilized, is in the construction of pass cards and card readers of the type disclosed in the last said patent. By predisposing the magnetized wires in certain patterns on or within the passcards, the cards may be, in effect, coded to produce different pulse responses when the cards are passed into or through a slot having permanent magnets and pick-up coils provided in the area through which the wire patterns of the cards may be passed adjacent the permanent magnets. By varying the patterns of the magnetized wires in a series of cards, each card may be made to identify a particular individual to whom it may be issued, and may be employed to pass such individual through one or more pre-selected barriers having readers responsive to the particular pulse arrangement generated by passing that particular card through or into the reader. Such cards may also be utilized for other identification purposes, such as operating a time-clock for each particular individual, for payroll purposes or otherwise in a system to account for the presence or absence of each individual holding a distinctive card.
The principal problem in utilizing the card and reader system disclosed in said U.S. Pat. No. 3,783,249, has been the practical one of fabricating such cards both from a cost standpoint and from the standpoint of insuring the operability of each card of a particular sequence of fabricated cards. Because the magnetized wires are small, considerable care must be exercised in disposing them upon, and securing them to, either the passcard itself, or to a small carrier sheet to be placed in or on such passcard. In practice, it appears that the more popular method of fabricating passcards of this type has involved placing the wires on or between small thin plastic sheets which are then inserted into a recess provided in the plastic passcard, or which sheets may be sandwiched between laminations of such passcard, or even simply placed upon the face of such passcard.
In order to increase the pattern variants for the wires, one of the techniques utilized heretofore has been to punch out portions of the sheet on which the wires have been laid and secured. Where this done, however, it becomes most critical for the insert to be properly disposed within or upon the pass-card. This is because in those security systems where each card is provided with a different coding to designate a different individual, it is necessary that the pulse pattern which is created by the insertion of each card into the reader, be exactly that needed to trigger the appropriate security system response.
Heretofore, where cards constructed in accordance with said U.S. Pat. No. 3,783,249 have been made either by providing different lengths of wires or different dispositions of the wires upon a sheet backing, which is then inserted in or otherwise applied to the pass-card, any mishandling of the small sheet after the wires have been secured to it, such as inserting the sheet upside down, renders it most difficult to detect, and may require review of an entire sequence cards numbering as much as thousands. Similarly, if it should be found that one of the wires placed on the backing sheet has been inadequately magnetized, the same problem of detection may be encountered. Additionally, where uniform lengths of wires are placed on the backing sheet and segments of the wire with the backing sheet are punched out, the same error in assembly may occur, with the consequent problem of having to ascertain from the entire sequence of cards, which one is defective. Where defective cards are located, unless a new card is individually made, a blank must then be recorded in the card sequence. All of these problems have tended to render the manufacture of pass-cards utilizing the principle disclosed in U.S. Pat. No. 3,783,249 quite costly, thereby limiting their use to very special security systems where such high cost can be justified from a business or other standpoint.
As used in the prior art, a magnetic wire could not be programmed after insertion in a passcard and the card was encoded by variation in physical placement of the wire on the passcard relative to the anticipated position of the magentic read head. Each magnetic wire on a passcard, however, was indistinguishable from any other wire on a passcard except for their relative positioning.
The encoding of such cards was permanent once the card was assembled. In one method, taught in U.S. Pat. No. 4,187,981, issued Feb. 12, 1980 to Siuko et al., the card was encoded by punching holes through the card to cut the wires into unequal segments disposed in a predetermined pattern. This form of encoding is also permanent and unalterable.
It is known in the prior art to provide magnetizable portions in a passcard, which portions may be alternately magnetized or demagnetized by a read head for storing and erasing information. This result is achieved by magnetizing a metallic portion of the card and using this magnetic field to cause movement of a lock element in the read head. Bi-stable magnetic wires are not used in such passcards. However, the read heads used in such a system are of fundamentally different operation from those necessary to read passcards using bi-stable magnetic wires. Thus, one known type of read head of the prior art uses tumblers which are operated by the coded magnetized portions of a passcard to clear a path for insertion of the card to activate a microswitch.
The read heads for decoding bi-stable magnetic wire patterns have no moving parts and operate by electronically decoding a series of pulses derived by passing the card through an external magnetic field in the read head. Heretofore, it has not been possible to alter the information encoded on a passcard using bi-stable magnetic wires as the encoding medium.
The readers of the type just described are currently in use and except as modified by the addition of magnetic coils to take advantage of the programmable data storage of of this invention, the readers are known in the art.